Fitness, muscle and fasted training
Read the training studies closely: separate fuel use, muscle size, strength, food intake and recovery before drawing a conclusion.
FASTING FREE / EDUCATION
A clearer view of fasting research.
Understand the basics. Explore the questions that matter in daily life. Go deeper into the science with clear lessons, practical examples, and original research.
FOLLOW THE CLAIM TO THE PAPER
Better questions.
Deeper evidence.
Fitness, prolonged fasting, and ketogenic diets deserve more than a headline. Examine what was tested, compare the findings, and read the original papers.
Prolonged fasting: read the evidence beyond the headline
A close reading of multi-day fasting studies, body composition, inflammatory signals, supervision and what happens when eating resumes.
Ketogenic diets: metabolism, health, and performance
Follow the evidence from measured ketosis to appetite, blood glucose, LDL and ApoB, exercise performance, and medication safety.
Original trials, research reviews, and scientific guidance—with methods, access notes, and limitations beside the claims. How we select evidence
PUT THE RESEARCH TO USE
Read. Question. Keep exploring.
Build a useful habit of asking what the evidence actually supports.
PRACTICE
Follow a claim through the evidence.
Work through the participants, comparison, measurements, and conclusion of a real research question.
Explore the claim checksKEEP YOUR CONTEXT
Come back to a paper with your questions.
Choose what to save in this browser. Keep your notes beside the current findings, limitations, and sources.
Open saved readingPREPARE A CONVERSATION
Bring useful questions to the discussion.
Choose and edit questions for a clinician, dietitian, or coach, then print a focused sheet with references.
Build a question sheetFOLLOW THE EDITORIAL WORK
See what changed and what was reviewed.
Read the collection history, known source corrections, and the current editorial and clinical review status.
See evidence updatesTHE LEARNING CENTER
Understand the why
behind fasting.
Build your understanding one lesson at a time. Clear explanations, everyday examples, and the evidence behind the advice.
New to the subject? Start here
Read the first lesson Fasting: the foundations
Understand the patterns, the questions researchers can answer, and the limits of a fasting timer.
A PLACE TO BEGIN
Follow a learning path.
Read in order, or go straight to the question on your mind.
PATH 014 lessons
Build a solid foundation
Understand the language, the safety questions, and why food quality still matters.
PATH 024 lessons
Connect the science to daily life
Explore meal timing, hunger, training, sleep, and schedules that do not fit a textbook.
PATH 034 lessons
Become a more confident reader
Understand metabolic measures, life-stage questions, longevity claims, and research headlines.
YOUR QUESTIONS, EXPLAINED
Explore every lesson.
Each lesson includes a practical example, a moment to reflect, and links to its sources.
12 lessons to explore
Start with the basics
4 lessonsFasting: the foundations
Understand the patterns, the questions researchers can answer, and the limits of a fasting timer.
Safety, medicines, and a better clinical conversation
Learn which questions a fasting resource cannot answer and how to prepare for an informed discussion with a clinician.
What belongs inside the eating window?
Understand meal quality, food variety, and adequacy before deciding whether changing the clock is useful.
Weight, calories, and the role of timing
Understand what weight-loss trials reveal about eating windows, energy intake, and changes in body composition.
Make sense of everyday life
4 lessonsMeal timing and your daily rhythm
Explore early and late eating, circadian research, and why the most useful question goes beyond window length.
Hunger, hydration, and knowing when to stop
Separate ordinary appetite questions from symptoms that should not be treated as a fasting challenge.
Training, recovery, and muscle
Learn why training goals, enough food, and recovery belong alongside any conversation about fasting.
Sleep, body clocks, and shift work
Explore why timing research becomes more complicated when sleep and work happen at unusual or changing hours.
Go deeper into the science
4 lessonsGlucose, insulin, and metabolic health
Learn what metabolic studies measure and how to distinguish a promising marker from a demonstrated health outcome.
Women, life stages, and the limits of general advice
Interpret the evidence without treating all women, or every stage of life, as one interchangeable population.
Autophagy and longevity: what the evidence can say
Follow the evidence from cellular recycling to emerging human measurements, and see where claims outrun the research.
Make sense of a fasting headline
A practical method for reading a trial, interpreting uncertainty, and checking whether a headline matches the evidence.
GO TO THE ORIGINAL RESEARCH
Follow a question through the evidence
Three short routes through the original sources. Read them alongside the lessons above.
Start with the basics
Understand the terms, then put nutrition and safety around the clock.
Does timing add anything?
Start with a review, then compare a year-long trial with a matched-calorie experiment.
Follow a headline to the evidence
Read a news story beside its original study, then see how a study plan is documented.
ORIGINAL SOURCES, WITH CONTEXT
Browse the source library
Search a question, author, condition, or DOI.
Your reading view
Choose two or three sources using Compare on the cards below.
Opening a summary keeps this view with you. A copied view link includes the search, filters, and selected sources.
TEMPUS: eating windows, exercise, and liver fat
Clavero-Jimeno et al. · Nature Communications
MRI-measured liver-fat change, the primary outcome, did not clearly differ between the active interventions and usual care, or between active groups.
Randomized controlled trial
187 randomized · 12 weeks for the primary outcome
Glucose evidence in prediabetes and type 2 diabetes
Viple et al. · Diabetologia
The overall HbA1c estimate was −0.30 percentage points (95% confidence interval: −0.63 to 0.02), which did not establish a clear difference. Fasting glucose was modestly lower.
Systematic review and meta-analysis of randomized trials
10 randomized trials; 599 participants · Average follow-up about 4 months
Evidence search through August 5, 2025
The 2026 AHA update: food quality beyond the clock
Lichtenstein et al.; American Heart Association · Circulation / American Heart Association
Updates the AHA’s 2021 statement. Emphasizes a lasting dietary pattern with varied plant foods, whole grains, appropriate protein sources, and replacing saturated fats with unsaturated sources.
Institutional scientific statement
PCOS: time restriction and calorie restriction compared
Corapi et al. · Nature Medicine
Both active approaches reduced weight compared with control. Weight change did not clearly differ between time restriction and calorie restriction.
Randomized controlled trial
76 randomized · 6 months
Cochrane’s review in the news
Cochrane communications; Mia Parkinson · Cochrane
Introduces the review’s comparison with regular dietary advice. The linked review explains which outcomes were assessed and how certain the evidence was.
Research news about a systematic review
Cochrane: little clear advantage over dietary advice
Garegnani et al. · Cochrane Database of Systematic Reviews
Compared with regular dietary advice, fasting may produce little or no additional weight loss or quality-of-life improvement. The evidence for these outcomes was low certainty.
Systematic review of randomized trials
22 studies; 1,995 participants · Reported outcomes up to 12 months
Evidence search through November 5, 2024
SGLT2 medicines: why ketogenic-diet safety needs context
Boehringer Ingelheim Pharmaceuticals, Inc. · DailyMed, U.S. National Library of Medicine
The label identifies ketogenic diets, reduced food intake, illness, and volume depletion among conditions that can precipitate ketoacidosis. Glucose may be below the levels usually expected with ketoacidosis.
Official prescription-drug labeling
Earlier windows look promising; shorter is not always better
Chen et al. · BMJ Medicine
Earlier windows generally performed better than later windows for some metabolic outcomes. Results did not consistently favor the shortest eating windows.
Systematic review and network meta-analysis of randomized trials
41 randomized trials; 2,287 participants · 4–48 weeks; median 8 weeks
Evidence search through January 3, 2023
How fasting strategies compare with continuous restriction
Semnani-Azad et al. · The BMJ
Benefits were broadly similar to continuous restriction. Alternate-day fasting showed a small additional weight difference, concentrated in shorter trials.
Systematic review and network meta-analysis of randomized trials
99 randomized trials; 6,582 participants · Varied; most trials were shorter than 24 weeks
Evidence search through November 14, 2024
Resistance training before or after breakfast
Vieira et al. · International Journal of Sport Nutrition and Exercise Metabolism
Both groups improved muscle thickness and strength without clear between-group differences in those outcomes.
Randomized controlled trial
37 recruited; 28 completed, including 22 women · 12 weeks
A human autophagy signal, with important limits
Bensalem et al. · The Journal of Physiology
An exploratory six-month comparison favored the combined intermittent approach over standard care. There was no significant increase from baseline within that group, and a decline in the control group may partly explain the difference.
Exploratory analysis within a randomized trial
121 participants in this analysis · 6 months
Inflammation and platelet signals during prolonged fasting
Commissati et al. · Molecular Metabolism
Inflammatory and platelet-activation markers increased. Urinary 11-dehydro-TXB2 remained elevated after refeeding. These were biological signals, not observed rates of thrombosis or cardiovascular events.
Single-arm clinical study with exploratory molecular analyses and external cohort comparisons
20 participants; untargeted proteomics in 15; targeted clinical and urinary measures in 20 · Mean 9.8 days of water-only fasting, followed by mean 5.3 days of supervised refeeding
Eating windows during a muscle-building study
Blake et al. · Journal of the International Society of Sports Nutrition
Both groups gained fat-free mass. TRE completed fewer repetitions and gained less fat; squat findings varied by analysis.
Small randomized controlled trial
17 participants · 8 weeks
The 4:3 trial included intensive behavioral support
Catenacci et al. · Annals of Internal Medicine
The 4:3 group lost about 2.9 kg more than the daily-restriction group at one year.
Randomized controlled trial
165 randomized; 125 completed · 12 months
Read beyond the weight-loss headline
National Institute on Aging · National Institutes of Health
This headline emphasizes weight change. The original trial’s primary outcome was visceral fat, which did not clearly differ between groups. Read both together.
Research news about a human randomized trial
Early, late, or self-selected: the primary outcome matters
Dote-Montero et al. · Nature Medicine
The main outcome, MRI-measured visceral fat, did not clearly differ between groups. Weight decreased more in the eating-window groups as a secondary outcome.
Randomized controlled trial
197 randomized · 12 weeks
Seven-day fasting: strength and endurance respond differently
Kolnes et al. · Nature Communications
Measured leg strength was unchanged, while absolute peak oxygen uptake fell 13% and exercise performance declined. Lean-mass estimates also decreased.
Small uncontrolled physiological intervention
15 initially included; 13 completed, including 7 men and 6 women · 7-day water-only fast; performance tested on day 6 and body composition on day 7
NIH explains the TIMET results
NIH Research Matters · National Institutes of Health
A plain-language introduction to the TIMET trial and its modest metabolic findings. Follow the linked original paper for the comparison group, effect size, and uncertainty.
Research news about a human randomized trial
What a mouse lifespan experiment can—and cannot—tell us
Di Francesco et al. · Nature
Dietary restriction extended lifespan in these mice, while genetic differences strongly influenced survival. Changes in common health markers did not reliably predict lifespan.
Randomized animal experiment
960 randomized; 937 started the diets at 6 months of age · Followed across the animals’ lifespans
TIMET: a modest glucose change with usual care
Manoogian et al. · Annals of Internal Medicine
HbA1c improved by an additional 0.10 percentage points on average (95% confidence interval: −0.19 to −0.003). The effect was small.
Randomized controlled trial
122 randomized; 108 completed · 3 months
Explore public dietary data—and its limits
CDC / National Center for Health Statistics · NHANES, with USDA dietary methodology
Provides food, nutrient, and eating-occasion information for population research. Documentation explains survey weights, recall methods, and changes in interview mode.
Observational survey data; no assigned intervention
Depends on the selected files, valid recalls, and analysis exclusions · August 2021–August 2023 collection; 24-hour dietary recalls
ISSN: keto, exercise performance, and body composition
Leaf et al.; International Society of Sports Nutrition · Journal of the International Society of Sports Nutrition
Endurance outcomes were generally unchanged or worse with keto; maximal-strength outcomes were commonly similar. Greater fat oxidation did not establish better performance. Energy, protein, and fluid differences complicate body-composition findings.
Professional position stand based on a review of controlled exercise studies
Evidence synthesis; no new participant cohort · Mostly short interventions; strength evidence discussed primarily spans 4–12 weeks
When researchers supplied the same calories
Maruthur et al. · Annals of Internal Medicine
Weight and glucose outcomes did not clearly differ. The weight difference was 0.3 kg, with a 95% confidence interval from −1.2 to 1.9 kg.
Randomized controlled feeding trial
41 randomized and completed · 12 weeks
Seven days of fasting: a changing blood proteome
Pietzner et al. · Nature Metabolism
Many measured proteins changed, with a broad pattern emerging after several days. Mean weight fell 5.7 kg; much of the measured lean-mass decrease reversed during the brief refeeding follow-up.
Small, uncontrolled human intervention with exploratory proteogenomic analyses
12 participants: 5 women and 7 men · 7-day water-only fast; measurements through 3 days after eating resumed
Eating windows and calorie restriction in type 2 diabetes
Pavlou et al. · JAMA Network Open
The eating-window group lost weight compared with control. HbA1c fell similarly with time restriction and calorie restriction; neither clearly outperformed the other for HbA1c.
Randomized controlled trial
75 randomized · 6 months
Energy availability, recovery and athlete health
Mountjoy et al. · British Journal of Sports Medicine
Prolonged or severe under-fueling can impair multiple body systems and performance.
Expert consensus informed by athlete research
What a small prolonged-fasting literature can tell us
Ezpeleta et al. · Nutrition Reviews
Short-term weight and some marker changes were reported, with variable lipid results and limited evidence of lasting improvements.
Narrative review of human water-only and Buchinger fasting studies
8 studies; only 2 measured changes in fat and lean mass · Fasting interventions of approximately 5–20 days; limited later follow-up
Healthy Heroes: eating windows for firefighters
Manoogian et al. · Cell Metabolism
A shorter eating window was feasible. Overall weight and glucose outcomes did not clearly differ between groups; some favorable findings came from exploratory higher-risk subgroups.
Randomized controlled trial
150 randomized; 137 completed · 12 weeks
What changes when identical meals move later?
Vujović et al. · Cell Metabolism
Later meals increased hunger, reduced energy expenditure during waking hours, and altered pathways measured in fat tissue.
Randomized crossover laboratory trial
16 completed both conditions · Two short inpatient protocols; meal schedules tested on days 3–6
An early window alongside weight-loss support
Jamshed et al. · JAMA Internal Medicine
The early-window group lost about 2.3 kg more weight. The primary body-fat outcome did not differ significantly in the main analysis.
Randomized controlled trial
90 randomized · 14 weeks
Keto-Med: glucose and lipids tell different stories
Gardner et al. · The American Journal of Clinical Nutrition
The primary HbA1c comparison did not show a clear difference (P = 0.11). Mean triglyceride changes were −16% versus −5%, while LDL cholesterol changed +10% versus −5%, for ketogenic versus Mediterranean-plus diets. These are relative changes from baseline.
Randomized crossover dietary trial
Publication cohort: 42 randomized, 40 started, 33 with complete primary-outcome data · Planned 12 weeks per diet, then 12 weeks of follow-up; some phases extended during COVID-19
Does an eating window add to calorie restriction?
Liu et al. · New England Journal of Medicine
Adding the eating window did not produce a clear additional reduction in weight, body fat, or metabolic risk markers.
Randomized controlled trial
139 randomized; 118 completed follow-up · 12 months
Daytime meals during simulated night work
Chellappa et al. · Science Advances
Daytime eating prevented the glucose-tolerance disruption seen with day-and-night meals during this laboratory protocol.
Randomized controlled laboratory experiment
19 participants · 14-day laboratory protocol
Read the TIMET study plan alongside its results
University of California, San Diego; TIMET investigators · ClinicalTrials.gov document archive
Describes eligibility, assignment, measurements, and consent. Comparing dated plans with the published report helps readers distinguish planned work from observed results.
Human trial protocol and consent document; not results
Planned maximum: 144; this is not the final randomized count · Planned 12-week intervention
The 2021 dietary statement, updated in 2026
Lichtenstein et al.; American Heart Association · Circulation / American Heart Association
A historical reference for the AHA’s dietary guidance, emphasizing overall food quality. For the updated statement in this collection, read the linked 2026 publication.
Institutional scientific statement
A controlled look at LDL and ApoB on keto
Burén et al. · Nutrients
Compared with control, the ketogenic diet increased LDL cholesterol by 1.82 mmol/L (95% CI 1.24–2.39) and ApoB by 0.50 g/L (95% CI 0.35–0.65). Both large and small LDL cholesterol fractions increased.
Randomized crossover controlled feeding trial
24 randomized; 17 completed both diets · Four weeks per diet, separated by a 15-week washout
Ketosis, appetite, and measured calorie intake
Hall et al. · Nature Medicine
Energy intake was 689 ± 73 kcal/day lower on the low-fat diet over two weeks (mean ± SE; P < 0.0001). Ketosis was established on the ketogenic diet. The difference in total body fat lost between diets was not statistically clear (P = 0.085).
Randomized inpatient crossover feeding trial
21 randomized; 20 completed and were analyzed · Two weeks per diet; four continuous inpatient weeks
The TREAT trial: an eating window without calorie targets
Lowe et al. · JAMA Internal Medicine
Weight change did not differ clearly between groups. The estimated difference was −0.26 kg, with a 95% confidence interval from −1.30 to 0.78 kg.
Randomized controlled trial
141 randomized; 116 provided data · 12 weeks
Diabetes: plan around medication and glucose risks
NIDDK interview with Martin M. Grajower, MD · National Institute of Diabetes and Digestive and Kidney Diseases
Explains why fasting can cause low glucose, high glucose, and dehydration, and why plans need to account for medicines and individual circumstances.
Official professional education interview
Start here: what fasting research is asking
NIH News in Health · National Institutes of Health
Introduces common fasting patterns and the difference between eating timing and food quality. It advises discussing fasting with a health professional, particularly when pregnancy, breastfeeding, diabetes medicines, or other risks are involved.
Official public education article
Eating windows and resistance training in women
Tinsley et al. · The American Journal of Clinical Nutrition
Muscle and performance improved across groups. A fat-mass difference appeared only in the per-protocol analysis.
Randomized controlled trial
40 randomized; 24 in the per-protocol analysis · 8 weeks
A large clinic cohort studying modified Buchinger fasting
Wilhelmi de Toledo et al. · PLOS ONE
Several short-term measurements and well-being scores improved. Two participants were hospitalized. This was modified fasting, not a water-only intervention.
Prospective observational clinic cohort
1,422 participants selected from 3,929 admissions · 4–21 days; duration groups were chosen rather than randomly assigned
Early eating in a small, controlled experiment
Sutton et al. · Cell Metabolism
Insulin sensitivity and some cardiovascular markers improved during early eating without weight loss.
Randomized crossover trial
8 participants · 5 weeks per condition
Adverse events in a supervised water-only fasting program
Finnell et al. · BMC Complementary and Alternative Medicine
Most recorded events were mild or moderate; two visits involved hospitalization, for dehydration and hyponatremia. A grade-3 event was the highest grade in 212 visits.
Retrospective observational chart review; no randomized comparison
768 qualifying visits from 652 patients · Fasts ranged from 2–41 days; median 7 days; analysis included supervised refeeding
NICE guidance on assessment and refeeding risk
National Institute for Health and Care Excellence · NICE
Risk assessment considers nutritional intake, weight history, body size, electrolytes and other clinical factors. High-risk care requires appropriately trained professionals.
Clinical guidance for nutrition support and risk assessment
Protein and the response to resistance training
Morton et al. · British Journal of Sports Medicine
Additional protein modestly improved average gains alongside training.
Systematic review and meta-analysis of randomized trials
49 trials; 1,863 participants · Training interventions lasting at least 6 weeks
Evidence search through January 2017
More fat oxidation, a higher oxygen cost
Burke et al. · The Journal of Physiology
Fat oxidation rose, but oxygen cost increased at race-relevant speeds. Race performance improved 6.6% and 5.3% in the carbohydrate-supported groups; the ketogenic estimate was −1.6% (90% CI −8.5% to 5.3%), with no clear improvement.
Controlled feeding and training intervention; preference-based allocation
21 individual athletes; 29 diet-camp datasets and 26 paired race datasets · Three weeks of intensified training, with testing before and after
An eating window alongside resistance training
Moro et al. · Journal of Translational Medicine
Fat mass decreased more with time restriction. Fat-free mass and maximal strength were maintained in both groups.
Randomized controlled trial
34 randomized · 8 weeks
Measuring fuel use over one day
Iwayama et al. · EBioMedicine
Pre-breakfast exercise increased 24-hour fat oxidation in this experiment.
Randomized repeated-measures laboratory experiment
10 participants · Four separate 24-hour calorimetry conditions
Fasted cardio and measured fat loss
Schoenfeld et al. · Journal of the International Society of Sports Nutrition
Both groups lost weight and fat; the study did not detect a difference between groups.
Small randomized controlled trial
20 randomized · 4 weeks
THE BIGGER PICTURE
Topics at a glance
Open a topic for a short synthesis and its sources.
Weight & body composition
Compared with what?
An eating window may change weight, but the comparison matters: unchanged eating, calorie restriction, and intensive support are different tests. Results vary across these settings.
Timing & daily rhythms
A window is only part of the picture
Timing studies do not consistently separate the clock from changes in calories and habits. Earlier eating is being studied; the evidence does not identify a single best window for everyone.
Glucose & metabolic health
Small changes need context
Glucose findings depend on the population and treatment. Short-term biomarker changes are different from preventing diabetes, and people taking glucose-lowering medicines need individual clinical planning.
Safety & nutrition
Nutrition and safety come first
A clock does not assess nutritional adequacy, medication risk, pregnancy, or individual health. Official education and nutrition guidance help put the trial results in context.
Exercise & muscle
Muscle needs more than a meal schedule
Training, food intake, and the population studied matter when interpreting body-composition findings. A short trial that maintains lean mass does not establish a long-term muscle or performance advantage.
Ketogenic diets
Keep the outcome in the question
Ketosis, energy intake, glucose, lipid markers, and performance are distinct outcomes. Compare the actual diets and populations before turning a favorable result for one measure into a general claim about health.
Prolonged fasting
A longer fast is a different intervention
Multi-day fasting studies often involve small, selected groups and clinical supervision. Changes in weight, blood proteins, or inflammation do not establish lasting benefit or a safe home protocol.
Sleep & shift work
Shift work changes the question
Controlled night-work experiments and trials in working firefighters answer different questions. Early findings support studying meal timing; they do not supply a universal fasting schedule for every shift.
Aging & longevity
A cellular signal is not a lifespan result
Exploratory human research can measure autophagy in particular cells, while animal experiments can study lifespan. Neither gives an app a personal autophagy clock or establishes that fasting extends human life.
Understanding evidence
Read the outcome, not just the headline
Check the primary outcome, comparison group, follow-up, and uncertainty. A registry describes a study plan, a dataset records observations, and news explains research; each serves a different purpose.
READ WITH CONTEXT
What makes evidence useful?
These summaries help you read public research. They do not choose an eating schedule or treatment for you. For health or medication decisions, use the safety information and discuss your circumstances with a qualified clinician.
Research glossary and three worked examplesCompare like with like
Ask who participated, what the comparison group did, and how long the study lasted. An eating window plus counseling is a different intervention from an eating window alone. A randomized trial can test an intervention; a survey association may also reflect other differences between people.
Look for the main outcome and uncertainty
The primary outcome is the question the trial was designed around. Other outcomes can be useful, but a favorable secondary result does not replace a null primary result. A confidence interval shows uncertainty around an estimate. For a difference, an interval crossing zero does not establish a clear difference. “No clear difference” also does not prove the approaches are identical.
Check whether HbA1c is reported as an absolute change in percentage points or as a relative percentage change, and keep the paper’s units. A change from 6.0% to 5.9% is an absolute decrease of 0.1 percentage points. A biomarker change is not automatically a reduction in future illness.
Check the date behind a review
A review’s publication date and its evidence-search cutoff can be years apart. We display both when verified. Reviews may include overlapping trials, so their participant counts must not be added together as independent evidence.
Know what kind of document you are reading
Guidance, scientific statements, protocols, datasets, and news have different purposes. A white paper is a document format, not a guarantee of scientific quality. Check authorship, methods, cited evidence, funding, and conflicts in the original document. Our news entries link to their underlying research; they do not count as extra studies.
How this collection is maintained
Fasting Free selects relevant original trials, systematic reviews, official health education, and public research resources. Each record includes the source, publication date, access status, a short finding, and limitations. We label animal work separately and preserve corrections and early-publication status where identified.
The lessons connect these sources with additional primary research and official education references. The research guides take specific claims back to original papers, with design comparisons, measured outcomes, access notes, and verified funding disclosures where available. Section citations identify supporting material. Hypothetical examples illustrate ideas; they are not patient results. Reading times are estimates based on article length.
This is a curated collection, not an exhaustive systematic review or a clinical guideline. “Checked” means the cited source and summary were reviewed for this collection, not that a clinician reviewed your health. The collection was updated November 5, 2026; each source retains its own check date.